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Question

 pure acid is to be added to a 10% acid solution to obtain 90l of 39% solution. what amounts should be used?

 

How many liters of 100% to  make solution??

How many liters of the 10% solution should be in the mixture??

Answer 1

If x = amt of pure acid and y = amt of 10% acid solution, then we know that

 

x + y = 90 (the total volume of the mixture)

 

We also know that

 

x + .10y = .39(90)   This is the total concentration of the mixture of acid solutions. We convert each percentage to a decimal. Of course, 100% = 1, and 10% = 0.10 and 39% = 0.39

 

Now, let's solve the first equation for y

 

x + y = 90

 

y = 90 - x   We can plug this into the second equation 

 

x + .10(90 - x) = .39(90)

 

x + 9 - .10x = 35.1

 

.9x + 9 = 35.1

 

.9x = 26.1

 

x = 2.9

 

We need to use 2.9 L of pure acid, and 90 - x = 90 - 2.9 = 87.1 L of 10% acid